Orthodontic brackets are a component of orthodontic systems for correcting malpositioned teeth. Orthodontic treatment using such systems generally involves the application of mechanical forces to urge malpositioned teeth into correct alignment. In conventional treatment, orthodontists or their assistants affix orthodontic brackets to a patient's teeth and engage an archwire into an archwire slot in each bracket. The archwire applies mechanical forces that coerce the teeth to move into a desired position. Traditionally, ligatures are employed to retain the archwire within each bracket's archwire slot. But ligatures may be difficult to handle and apply so as to secure the archwire to the brackets. To overcome these difficulties, self-ligating orthodontic brackets have been developed that eliminate the need for separate, individual ligatures by relying on a movable ligating member on the bracket, such as a latch or a slide, which in a closed position overlies the archwire slot thereby retaining the archwire within the bracket's archwire slot. In this regard, the bracket body may include a track or passageway configured to receive the ligating member therein and facilitate the movement of the ligating member between an opened and closed position.
Conventional manufacturing processes for orthodontic brackets include metal injection molding (MIM) and ceramic injection molding (CIM) for metal and ceramic brackets, respectively. In each of these processes, metal or ceramic particles are mixed with a binder and then injected into a mold having the shape of an orthodontic bracket. The intermediate body resulting from the molding process is typically oversized compared to the final product. The intermediate body is then sintered to remove the binder and form either a metal or ceramic orthodontic bracket. The intermediate body typically shrinks during the sintering process to arrive at the desired size of the orthodontic bracket.
The conventional molding process in the MIM or CIM process is typically a single shot process. Thus, the configuration of the various features of the orthodontic bracket may be limited by such a single shot molding process. In this regard, various features of the bracket, including, for example, the archwire slot, the passageway for the ligating member, an overshoot cavity configured to capture an end of the ligating member, or other features may not be capable of being formed from a single shot molding process. Accordingly, these features, if desired in the orthodontic bracket, are typically formed through a post-formation process. Such post-formation processes are generally time consuming and expensive.
Some molding apparatus have increased in their complexity and may include a movable slide extendable from the wall of the mold cavity and capable of moving into and out of the mold cavity so as to form various features in the molded body. Because the slide must be retractable from the mold cavity, or ultimately the molded body must be de-molded from the mold cavity, the slide has limited geometries. For example, the more distal portions of the slide (i.e., portions further from the wall of the mold cavity) must be narrower than more proximal portions of the slide (i.e., portions closer to the wall of the mold cavity).
This converging aspect in a proximal to distal direction then allows the slide to be retracted from the mold cavity, or allows the molded body to be de-molded from the mold cavity. In contrast, a diverging geometry (i.e., wider in a more distal direction) would not allow the slide to be retracted, or allow the molded body to be de-molded from the mold cavity. This limitation in the single shot molding process then limits the possible geometries of the bracket features capable of being formed by such movable slides. However, such alternative geometries of orthodontic bracket features not capable of being formed in a single shot molding process may be desirable to enhance use and functionality of the orthodontic bracket. For example, certain undercut formations, which include various voids or cavities, are not capable of being formed in a single shot molding process and thus are typically formed using post-formation processes.
There is a need, therefore, for self-ligating orthodontic brackets and associated methods for forming self-ligating orthodontic brackets that address these and other problems associated with conventional orthodontic brackets and manufacturing methods. More particularly, there is a need for an orthodontic bracket having undercuts or other features not capable of being formed in a single shot molding process and a method for making such an orthodontic bracket that avoids the high cost and increased time of making such undercuts or other features in post-formation processes.